Apparatus for drilling a borehole with a gaseous circulation medium



Dec. 24, 1968 D. P. NICHOLS APPARATUS FOR DRILLING A BOREHOLE WITH A GASEOUS CIRCULATION MEDIUM Filed June 5, 1966 FIG.2

DEAN R NICHOLS INVENTOR BY W ATTORNEY United States Patent 3,417,830 APPARATUS FOR DRILLING A BOREHOLE WITH A GASEOUS CIRCULATION MEDIUM Dean P. Nichols, Dallas, Tex., assignor to Mobil Oil Corporation, a corporation of New York Filed June 3, 1966, Ser. No. 555,101 6 Claims. (Cl. 175209) ABSTRACT OF THE DISCLOSURE This specification discloses a crossover sub to be used primarily in conjunction with reverse circulation drilling. The sub is internally vertically partitioned and has a packer journalled thereon, permitting the use of a drill bit with jet nozzles for efliciently removing cuttings while utilizing conventional drill pipe.

This invention relates to apparatus for drilling a borehole with air and/or gas as the circulation medium and efliciently removing the cuttings. More particularly, the invention relates to a novel drill string sub for utilizing reverse circulation of a gaseous drilling fluid, while directing the gas at the cuttings in the bottom of the borehole through a conventional jet drill bit and utilizing an otherwise conventional drill string arrangement.

One of the most pressing technical problems arising in the field application of air and/ or gas drilling is the excessive rate of bit wear if the cuttings are not efliciently removed from the bottom of the hole. This problem becomes more and more evident as the diameter of the hole increases beyond What is commonly described as slim hole drilling. Even when drilling a thirteen-inch diameter hole for setting surface casing, conventional circulation procedures are not advisable. When drilling twenty-fourto thirty-six-inch vertical shafts, for ventilation or communication, with horizontal underground shaftsfor mining oil shale or coal, complicated dual drill stems have been found necessary. (See Big Hole Drilling Technology Is Changing, H. L. Caldwell, World Oil, September 1965, pp. 103-107.)

The problems associated with drilling boreholes, with gas as a circulation medium, are due to the higher velocity necessary for the gas to lift the cuttings on the way back to the surface and the difliculty in forcing the gaseous medium to impinge directly on the cuttings. If these cuttings are not carried out of the hole efliciently, the drill bit will be worn down merely grinding up the old cuttings. Previous attempts to solve the problem of providing the necessary gas velocity have been concerned with the adaptation of reverse circulation, the gas being injected directly down the borehole and returning through the interior of the drill pipe. However, the gas and/or air tend to rise immediately into the stem of the drill pipe without actually touching the bottom of the borehole, therefore not impinging on the cuttings and not removing them. Regardless of the rising velocity of the fluid in the drill stern, such a device is ineffective if the cuttings remain substantially undisturbed in the bottom of the borehole.

These previous deficiencies in reverse circulation gas drilling have brought forth a number of suggestions directed to double-passage drill pipes, combined with a packer sealing off the lower end of the borehole to prevent the gas from returning through the annulus. The cheapest and most satisfactory of these (and probably the only ones actually built) have utilized concentric pipes, the smaller welded within the larger, to obtain the concentric passages. This general solution appears to be quite satisfactory from a technical standpoint, but it is economically unsatisfactory in that double-passage drill pipe is quite expensive when compared to the ordinary single-passage drill pipe and the seals between the passages at each drill pipe joint have to be inspected carefully and often replaced to permit the apparatus to work efficiently.

Therefore, it is one aspect of the present invention to provide a reverse circulation sub for drilling with gas which will permit the use of conventional drill pipe joints for all but the lowest sub.

Another aspect of the present invention is to provide a means for insuring that the circulating gas will impinge on the cuttings at the bottom of the borehole even though the annulus of the borehole is utilized to conduct the circulating gas down.

A further aspect of the invention is to provide a very large capacity accumulator for storing the gas under pressure prior ,to the gas being introduced into the drilling area adjacent the drill bit.

Other aspects and advantages of the invention will be readily apparent from the following description, when taken in conjunction with the accompanying drawings, which illustrate useful embodiments in accordance with this invention:

FIGURE 1 is an elevational view illustrating a drill string of the present invention suspended within a borehole and the necessary above-surface equipment; and

FIGURE 2 is an enlarged view of a novel crossover sub of the drill string illustrated in FIGURE 1, partially in cross section.

Referring first to the general showing of FIGURE 1, a drill string, generally designated 10, is illustrated as consisting of; a kelly 12, a plurality of conventional pipe joints 14, and a novel cross-over sub 16, connected between the lowest pipe point 14 (or drill collars) and a rotary drill bit 18, suspended in a borehole 20. The drill bit 18 may be of any of the types normally utilized with rotary drilling if the hole is not of a very large diameter (not over 18"), in this case being shown as a tricone roller bit having rollers 22 and fluid jet nozzles 24 (only one shown). When drilling large diameter holes special bits must be designed for cutting the large area of the borehole and directing the gas so as to efliciently impinge on the cuttings. A cemented-in surface casing 26 casinghead 28 and an above-mounted drilling head 29 lines the upper end of the borehole and is capped with a having a rotating seal (not shown) coacting with the kelly 12 which extends therethrough and which forms a substantially airtight slidable connection therewith. The drill pipe string 10, suspended in the borehole from a drilling rig 30 by means of a conventional swivel 32, is driven by a rotary table 34 ttuough the kelly 12.

Circulating gas is pressured up in a compressor 36 and discharged through an accumulator 38 into an inlet line 40 and through the drilling head 29 and then into the casinghead 28 from which it enters the upper end of the annulus 42 of the borehole 20. The gas is routed out of the borehole 20, as will be explained later, through the interior of the drill pipe string 10, and the gooseneck 44 of the swivel 32, and is directed by means of an interconnecting flexible line 46 into a cyclone separator 48. The separated-out gas then is conducted, by return line 50, back to the inlet of the compressor 36. The term gas as used herein is contemplated to encompass any gaseous fluid such as an inert gas, i.e., nitrogen, CO or air. The criteria for determining which gas is to be used is the pressure and content of the natural gas present in the well. If air is being used as the circulating fluid, as might well be the case, the compressor 36 would draw directly from the surrounding air; and in this case, rather than using a cyclone separator, the line 46 would be discharged to the atmosphere at a point distant from the drilling rig 30. When the circuit is designed for closed circulation, the cuttings from the drilling operation, entrained in the gas, drop through the separator 48, and into a settling tank 52 along with any liquids that might also have been carried up through the interior of the drill pipe string 10. Liquids may have been added, as vapor, to the gas stream, prior to injection into the annulus 42 of the borehole 20, to provide better lubrication of the rotary drill bit 18 or the liquid may be merely seepage which has settled to the bottom of the borehole 20 forming a slurry with the cuttings. The cuttings are removed from the settling tank 52 through an outlet port 54, while the liquid is drawn ofi through a separate outlet 56. If it is desirable to then reinject the liquid into the gas stream, this may be done through a port 58 in the casinghead 28.

In FIGURE 2 the novel crossover sub 16 is shown to consist of a tubular casing 60, similar in exterior configuration to a conventional drill pipe joint. The ends of the casing 60 are interiorly and exteriorly threaded to permit the crossover sub 16 to be inserted directly into and become a part of the drill string 10. A slidable packer is journalled on the pipe joint 60 of the crossover sub 16 by means of an axial bearing 71 and a pair of thrust bearings or washers 72 backed up by locating flanges 73 fixed to the pipe joint 60, to separate the areas of the annulus 42, above and below. A longitudinal divider 61 is fixed within the tubular casing 60 forming parallel conduits 62 and 63. The conduit 62, at the left (as shown in FIGURE 2) is open at its lower end and terminates at its upper end at a partition 64. An upper port 66, through the wall of the casing 60, just below the partition 64, provides communication between the annulus 42 of the borehole 20 above the packer 70- and the upper end of the left-hand conduit 62. The right-hand conduit 63 is open at its upper end and terminates at its lower end in a partition 67. Lower ports 68, through the wall of the casing 60, just above the partition 67, provide communication between the annulus 42 of the borehole below the packer 70 and the lower end of the right-hand conduit 63. The partition 61 is not necessarily centrally positioned as shown in FIGURE 2 but would probably be offset (to the left) to enlarge the conduit 63 to reduce the pressure drop in this conduit since the gas in the bottom of the borehole is almost at atmospheric pressure. In conjunction with the larger conduit 63, the plurality of ports 68 should have a composite area at least equal to the crosssectional area of the conduit 63 so that essentially no pressure drop is caused at that point.

The packer 70 consists of a rigid ring-shaped channel member 74, open along its periphery to the wall of the borehole 20. A continuous flexible boot 76 is fixed over the open face of the ring-shaped channel member 74. A weep hole 78, in the upper closed face of the ringshaped channel member 74, connects the interior of the packer 70 with the annulus 42 of the borehole 20, above the packer 70, so that at all times that the gaseous circulation fluid is being injected into the annulus 42 of the borehole 20, the packer 70 will be pressurized. The boot 76, consisting of a resiliently reinforced rubber material, well known in the art, will press directly against the wall of the borehole without internal pressurization of the packer 70. The internal pressure is necessary only to sustain the seal as the pressure above rises. If there is substantial initial leakage past the periphery of the boot 76, there will be no pressure differential between the sides of the boot 76 and the boot will never be sealed against the wall of the borehole 20. To avoid such a circumstance, the boot should have an original diameter at least equal to the diameter of the borehole. If it is felt to be desirable to utilize the same packer 70 over a range of boreholes, a separate pressurization system will be necessary. This would entail a pressure line connecting the weep hole with a separate compressor on the surface. Since the packer 70 does not rotate a simple fluid onne tion is all that 4 is needed. Such a system can be readily designed by those skilled in the art.

It is seen that the crossover sub 16 permits the pressurized gas, accumulated within the large annulus 42 of the borehole 20, to flow in needed amounts through the port 62 and down into a conventional rotary drill bit 18 therebelow. The packer 70 will slide down the borehole 20, as the drill pipe string 10 is lowered, without tending to rotate also, due to the packer 70 being rotatably journalled on the axial bearing 71 and being held between the thrust bearings or washers 72. The gas exits through the jet nozzles 24 of the rotary bit 18 and impinges on the bottom of the borehole 20, picking up the loose cuttings 80 and any collected fluids that may be forming a. slurry therewith. The cuttings 80, and any fluids, are then directed through the port 68, up through the conduit 63 in the crossover sub 16, and up into the interior of the drill pipe string 10. It is therefore possible for an ordinary drill pipe and rotary bit to be used, the only unconventional element being the crossover sub 16. The velocity of the gas necessary to carry the cuttings from the borehole is no longer dependent on the size of the annulus 42 between the drill string 10 and the walls of the borehole 20, even when using a conventional drill pipe string 10, but only upon the size of the interior passage of the drill pipe string 10 itself, which size may remain constant regardless of the size of the borehole 20'. It is usually desirable that a velocity of three thousand feet per minute be held for the returning gas, and this may easily be accomplished with conventional pumps even when using 13% inch casing as drill pipe (as has been successfully used by the Atomic Energy Commission when drilling 6-foot diameter holes). A casinghead pressure of 200 p.s.i. would be sufficient. In the event that a large amount of water flowed into a well being drilled by this process, one of the newly developed foam drilling fluids could be used. In fact there is no reason that a liquid drilling fluid could not be utilized with the novel crossover sub of the present invention under the proper circumstances.

At this time it seems desirable, and certainly simpler, to allow the packer to slide down the walls of the borehole while under pressure, as shown in FIGURE 2. If, however, the packer were showing undue wear after being in use for a time, one of the prior art step-motion packers such as shown in the Camp et al. Patent 2,951,680 could be substituted. This type of prior art packer, as well as being rotatably mounted upon the drill pipe, also slides along the sub, a length equal to the length of a drill pipe joint. When depressurizing the system for adding a new joint, the packer will deflate and drop to the lower end of its vertical travel. Upon repressurizing the packer by repressurizing the system, the packer will again grip the Walls and hold its position until the drill pipe has moved down the length of one drill pipe joint through the packer. A longer crossover sub, than that shown in FIGURE 2, would be needed for this modification.

Although the present invention has been described in connection with details of a specific embodiment thereof, it is to be understood that such details are not intended to limit the scope of the invention. The terms and expressions employed are used in a descriptive and not a limiting sense and there is no intention of excluding such equivalents, in the invention described, as fall within the scope of the claims. Now having described the apparatus herein disclosed, reference should be had to the claims which follow.

What is claimed is:

1. A novel crossover sub adapted to be connected operatively into a conventional drill string, comprising: a hollow tubular casing; means at each end of said casing to connect releasably said crossover sub to the end of a hollow tubular drill string element; packer means mounted on the outside of said casing and adapted to coact with the wall of a borehole to seal off the portion of a borehole annulus on a first side of said packer means from a portion of a borehole annulus on a second side of said packer means; means to pressurize said packer means in a borehole in conjunction with a circulation fluid being applied into a borehole under pressure on a side of said packer means whereby the pressure of the circulation fluid in a borehole, in which said crossover sub is used, pressurizes said packer means; a first port means in the wall of said casing on said first side of said packer means; a first conduit means between said first port means and the interior of said casing adjacent said releasable connecting means at a second end of said casing adjacent said second end of said packer means whereby fluid entering said casing of said crossover sub from a borehole annulus on said first side of said packer means is directed through the interior of said casing and into the interior of a drill string element releasably connected to said second end of said casing; a second port means in said wall of said casing on said second side of said packer means; and a second conduit means between said second port means and said interior of said casing adjacent said releasable connecting means at a first end of said casing adjacent said first end of said packer means whereby fluid entering said casing of said crossover sub from a borehole annulus on said second side of said packer means is directed, from a drill string element releasably connected to said second end of said casing, through the interior of said casing and into the interior of said drill string element releasably connected to the first end thereof.

2. A novel crossover sub adapted to be connected operatively into a conventional drill string, comprising: a hollow tubular casing; means at each end of said casing to connect releasably said crossover sub to the end of a hollow tubular drill string element; packer means mounted on the outside of said casing, said packer means being hollow and consisting in part of at least a flexible boot adapted to coact with the wall of a borehole to seal off the portion of a borehole annulus on a first side of said packer means from a portion of a borehole annulus on a second side of said packer means, a weep hole in said packer means forming a connection between a borehole annulus at one side of said packer means and the interior of said hollow packer means; a first port means in the wall of said casing on said first side of said packer means; a first conduit means between said first port means and the interior of said casing adjacent said releasable connecting means at a second end of said casing adjacent said second side of said packer means whereby fluid entering said casing of said crossover sub from a borehole annulus on said first side of said packer means is directed through the interior of said casing and into the interior of a drill string element releasably connected to said second end of said casing; a second port means in said wall of said casing on said second side of said packer means; and a second conduit means between said second port means and said interior of said casing adjacent said releasably connecting means at a first end of said casing adjacent said first side of said packer means whereby fluid entering said casing of said crossover sub from a borehole annulus on said second side of said packer means is directed, from a drill string element releasably connected to said second end of said casing, through the interior of said casing and into the interior of said drill string element releasably connected to the first end thereof.

3. A novel crossover sub adapted to be connected operatively into a conventional drill string, comprising: a hollow tubular casing; means at each end of said casing to connect releasably said crossover sub to the end of a hollow tubular drill string element; packer means; means for rotatably journaling said packer means on said casing between a first and a second port means in the wall of said casing whereby said packer means does not rotate during rotation of a drill pipe string within which said crossover sub is connected; said packer means being adapted to coact with the wall of a borehole to seal off the portion of a borehole annulus on a first side of said packer from a portion of a borehole annulus on a second side of said packer; a first conduit means between said first port means, at a first side of said packer means, and the interior of said casing adjacent said releasable connecting means at a second end of said casing adjacent said second side of said packer means whereby fluid entering said casing of said crossover sub from a borehole annulus on said first side of said packer means is directed through the interior of said casing and into the interior of a drill string element releasably connected to said second end of said casing; and a second conduit means between said second port means, on a second side of said packer means, and said interior of said casing adjacent said releasable connecting means at a first end of said casing adjacent said first side of said packer means whereby fluid entering said casing of said crossover sub from a borehole annulus on said second side of said packer means is directed, from a drill string element releasably connected to said second end of said casing, through the interior of said casing and into the interior of said drill string element releasably connected to the first end thereof.

4. Apparatus for rotary drilling utilizing a novel crossover sub releasably connected in a tubular hollow drill string just above a drill bit; means for adjustably suspending and rotating said drill string in a borehole; means for sealing the upper end of said borehole, said drill string extending through said sealing means; means for introducing a gaseous drilling fluid into said borehole annulus adjacent the upper end thereof; and means for directing said drilling fluid and suspended cuttings out of the interior of said drill string above the borehole, said crossover sub comprising: a hollow tubular casing; packer means mounted on the outside of said casing and adapted to coact with the wall of said borehole to seal off the portion of the annulus of said borehole on a first side of said packer means from a portion of said annulus of said borehole on a second side of said packer means; a first port means in the wall of said casing on said first side of said packer means; a first conduit means between said first port means and the interior of said casing adjacent said releasable connecting means at a second end of said casing adjacent said drill bit whereby fluid entering said casing of said crossover sub from said annulus of said borehole on said first side of said packer means, above said packer means, is directed through the interior of said casing and into the interior of a drill bit releasably connected to said second end of said casing; a second port means in said wall of said casing on said second side of said packer means, below said packer means; and a second conduit means between said second port means and said interior of said casing adjacent said drill string at a first end of said casing whereby fluid entering said casing of said crossover sub from a borehole annulus below said packer is directed, from said drill bit releasably connected to the lower end of said casing, through the interior of said casing and into the interior of said drill string releasably connected to the upper end of said casing.

5. Apparatus as recited in claim 4 wherein a drill bit is releasably connected into said drill string beneath said crossover sub, said drill bit being a jet drill bit whereby the fluid directed into said bit is jetted out in the vicinity of cuttings in the bottom of a borehole to remove said cuttings from the bottom of a borehole.

6. A novel crossover sub adapted to be connected operatively into a conventional drill string, comprising: a hollow tubular casing; means at each end of said casing to connect releasably said crossover sub to the end of a hollow tubular drill string element; packer means mounted on the outside of said casing, said packer means being hollow and consisting in part of at least a flexible boot adapted to coact with the wall of a borehole to seal ofi the portion of a borehole annulus on a first side of said packer means from a portion of a borehole annulus on a second side of said packer means; means for rotatably journalling said packer means on said casing whereby said packer means does not rotate during rotation of a drill pipe string within which said crossover sub is connected; a weep hole in said packer means forming a connection between a borehole annulus at one side of said packer means and the interior of said hollow packer means; a first port means in the wall of said casing on said first side of said packer means; a first conduit means between said first port means and the interior of said casing adjacent said releasable connecting means at a second end of said casing adjacent said second side of said packer means whereby fluid entering said casing of said crossover sub from a borehole annulus on said first side of said packer means is directed through the interior of said casing and into the interior of a drill string element releasably connected to said second end of said casing; a second port means in said wall of said casing on said second side of said packer means; and a second conduit means between said second port rneans and said interior of said casing adjacent said releasable connecting means at a first end of said casing adjacent said first side References Cited UNITED STATES PATENTS 1,764,488 6/1930 Zublin 166242 X 2,543,382 2/1951 Schabarum 175215 X 3,052,300 9/1962 Hampton 16684 3,109,501 11/1963 Pugh 175-325 NILE C. BYERS, JR., Primary Examiner.

U.S. Cl. X.R. 

